Pump

ABSTRACT

A minute quantity viscous material dispenser employing a pressurized material source and a reciprocating piston is driven by a variable drive which is controlled in response to a signal reflective of piston position and wherein the drive can be controlled for direction, stroke distance, speed, acceleration, and force and wherein the drive is coupled to the piston through a quick disconnect.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to dispensing systems and, more particularly, toa computer-controlled, small quantity dispensing system for depositingcontrolled amounts of viscous fluids on a work piece employing a linearactuator operated piston.

2. Description of the Prior Art

Accurately controlled depositation of small quantities of viscousmaterial on work pieces is an important part of the manufacturingprocess of many types of devices such as circuit boards and microcircuits. Such materials may include solder paste, adhesives, variousepoxies, electrically conductive materials, potting materials,insulating materials and the like. Accurate small quantity, high speeddeposition is also important in the medical fields for reagents,collegians, DNA samples and other fluids. While various systems anddevices have been proposed for dispensing such materials, includingdrop-at-a-time dispensers, one successful approach has utilized thecombination of a pressurized supply of material to a dispense chamberthrough which a piston moves to force predetermined quantities ofmaterial into a dispensing orifice. Such devices are shown, for example,in U.S. Pat. Nos. 4,572,103 and 4,941,428, the teachings of which areexpressly incorporated herein by reference.

In such devices, the material to be dispensed is introduced to acontainer which may be pressurized by, for example, a supply ofcompressed air and which communicates via a passageway to a pre-dispensechamber positioned above and in communication with a needle-likedispensing orifice member. A piston is mounted for movement through thepre-dispense chamber into a pumping chamber open to the pre-dispensechamber and the dispensing orifice member. Movement of the piston intothe pumping chamber forces material in the pumping chamber to movethrough the orifice member whereas withdrawal of the piston from thepumping chamber into the pre-dispense chamber permits a re-supply ofmaterial into the pumping chamber due to the pressurized supply from thecontainer.

Such dispensing devices may have the piston actuated by means of, forexample, a compressed air or hydraulic cylinder actuator. Adjustment ofthe amount of material to be dispensed per stroke of the piston can bemade by a stroke limiter attached to the piston which can bemechanically adjusted to limit the stroke length by providing a fixedstop affixed to the piston, or to the piston actuator, or by changingthe piston, pumping chamber and dispensing orifice for one of adifferent size.

While such devices have proven successful, they are limited in theirversatility. Volumetric dispensing modifications must either be made byadjusting the stroke length of the piston manually or by replacing thepiston, pumping chamber and orifice, either method creatingdisadvantages. Adjustments of the stop position require that thedispensing apparatus be interrupted in its cycle to allow access to theadjustment. Additionally, the adjustments are difficult to make withaccuracy since they rely upon a manual repositioning of the stop andfurther may require many test runs before the optimum dispense volume isarrived at. Because it may be desirable to dispense different quantitiesat different points on a single work piece, such manual adjustmentmechanisms are disadvantageous. Substitution of pistons and pumpingcylinders is likewise time intensive and difficult and may involvedisassembly of substantial portions of the device, a procedure that isdetrimental to optimization of production runs.

It would, therefore, be an advance in the art to provide improvedmethods and structure for modification of the dispense volume ofpressurized small quantity pump dispensers which allow rapidmodifications to dispense volume to be made.

It would be a further improvement in the art to provide methods anddevices allowing dispense volume modification to be made “on the fly”during operation of small quantity pre-pressurized piston pumpdispensers.

It would be a further improvement in the art to provide for ease ofremoval of the piston and pumping chamber of a small volume,pre-pressurized piston pump dispenser.

These and other improvements are obtained by the following describedinvention.

SUMMARY OF THE INVENTION

A small volume dispense pump is provided with a reciprocating pistonpositioned concentric with a pumping chamber which is open to apre-dispense chamber which in turn is supplied with material to bedispensed, the material being supplied under pressure. The pumpingchamber is also in communication with a dispensing tip or orifice.Reciprocation of the piston into the pumping chamber, after the pumpingchamber has been supplied with material from the pre-dispense chamber,acts in the manner of a hypodermic to force material through the pumpingchamber, the dispensing orifice member and out of the dispensing end ofthe orifice member. Upon withdrawal of the piston from the pumpingchamber, the pumping chamber will be refilled with material from thepre-dispense chamber. Devices of this type, shown for example in U.S.Pat. Nos. 4,941,428 and 4,572,103, are capable of repeatedly,accurately, dispensing minute quantities of material including highlyviscous material. As is known in the art, actuation of the piston may beeffectuated by a pneumatic cylinder which may in turn be controlled byan electro pneumatic control which in turn may be controlled by acomputerized control system. The computerized control system may providefor individual stroke operation of the pump, predetermined multiplestroke operation, operation for a period of time, or any combinationthereof.

Such dispensers are often employed with XYZ positioning control systemswhich may control either movement of the work piece, or of thedispensing orifice or a combination of both. By integrating control ofXYZ axis movements with control of piston operation, it is possible toprovide spot depositation of material, substantially continuous linedepositation of material, dotted line depositation of material, or areafill depositation of material. By using appropriate software, it ispossible to provide graphic depositation and to create pixel definedindices.

This invention controls operation of the piston through a variablestroke actuator which allows the piston to be moved by a controlledamount during the dispense cycle. In this manner, the dispense devicecan be adjusted automatically during operation to provide for a greateror lesser dispense quantity per stroke. Control of piston force mayaccommodate changing dispense needs such as might be encountered byvariations in material characteristics such as viscosity changes. Theinvention utilizes a computer control to move the actuator. The controlcan stop the piston's movement at any point in its travel and cancontrol direction, acceleration, speed and force. A piston positionsensor monitors piston movement, either directly or indirectly, andprovides signal input to the computer.

In a preferred embodiment, the piston is driven by an electronic linearactuator.

In an embodiment of the invention, a variable linear actuator iscontrollable to provide stroke length adjustment, velocity adjustment,change in velocity adjustment and force adjustment, all under computercontrol.

In an embodiment of the invention, the piston is coupled with a pistonposition sensor which provides an output signal indicative of therelative position of the piston which the computer control may utilizeto control further movement of the piston.

In an embodiment of the invention, a piston position sensor ismechanically coupled to the piston for movement therewith and has adetectable portion which passes in proximity to a variable outputsensor, the output of which can indicate piston position and be used todetermine relative change in position and rate of change in position ofthe piston.

In an embodiment of the invention, the piston is coupled to the linearactuator through a magnetic coupling allowing quick disassembly of anactuator sub-assembly from a dispensing sub-assembly therebyfacilitating change in piston and pumping chamber providing cleaning orfor quick changes in materials and/or dispense orifice size.

It is therefor an object of this invention to provide for controlledvariability during operation of a small volume reciprocating pistonviscous material dispenser utilizing a controllable linear actuatordriven piston.

It is another, and more specific object of this invention, to provide acomputer-controlled small quantity dispensing system for depositingcontrolled amounts of viscous fluids on a work piece utilizing a linearactuator operated piston in conjunction with a piston position andmovement sensor.

It is another object of this invention to provide a quick change smallquantity dispensing system for depositing controlled amounts of viscousfluids on a work piece utilizing separable actuator and dispensesub-assemblies coupled together through a magnetic coupling.

These and other objects of this invention will become apparent to thoseskilled in the art from the following detailed description of onepreferred embodiment, it being understood that many variations will beapparent to those of ordinary skill in the art in substitution for thespecific structures disclosed in the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a control system for a variablesmall quantity dispense system.

FIG. 2 is a cross-sectional view of the actuator sub-assembly anddispense sub-assembly.

FIG. 3 is a fragmentary enlarged sectional view of the piston positionsensor.

FIG. 4 is a partially schematic view similar to FIG. 2 illustratingde-coupling of the sub-assemblies.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 2, the dispenser 10 of this invention is particularlysuited for extremely small volume dispensing of viscous material, forexample, as would be utilized in manufacture of electronic componentssuch as circuit boards or microcircuits. Modern manufacturing techniquesemphasize extremely tight and controlled placement of minute quantitiesof liquid, semi-liquid and paste materials, such as, for example,fluxes, solder paste, silver, conductive epoxies, encapsulents,underfill, damfill materials, potting materials and the like which mayrange in viscosity from 300 centipoise to several million centipoise.Additionally, high speed manufacturing requires that the material bedispensed at extreme speeds, for example, from ten to one hundreddispense actions per second. With individual dot dispenses on the orderof five to forty mils in diameter of dispensed material per dispenseoperation, reliable supply of material is a critical factor.Importantly, since the pot life of some materials may be on the order oftwenty minutes, to a few days, and since viscosity and other materialchanges can take place during the pot life term, it has been found thatreciprocating pistons forcing material through a needle-like dispensetip present a particularly viable solution. Thus, the dispense device 10includes a needle-like dispense tip 11 projecting from the bottom of adispense sub-assembly 12 which receives a reciprocating piston 13. Thedispense subassembly 12 is provided with material from a materialreservoir 14 through a conduit 15 open to a pre-dispense chamber 16through which the piston 13 reciprocates. The material stored in thematerial reservoir 14 is acted upon by pressure such as may be supplied,for example, from an air pressure line 17. In this manner, the materialin the pre-dispense chamber 16 is maintained at greater than atmosphericpressure. The pressure may be adjusted by adjusting the air pressure atline 17 to accommodate materials of differing viscosities. It will beappreciated that although I have shown an air pressure materialreservoir, other methods of pressurizing may be utilized, such as, forexample a moving piston chamber, a screw feed or the like.

Piston 13 is preferably received in a piston guide bushing 18 whichterminates at the pre-dispense chamber in spaced relation to a pumpingchamber 19. The pumping chamber 19 is received interior of a fitting 20which may be affixed as the top-most portion of the overall dispense tip11 assembly. The pumping chamber is dimensioned to closely receive thepiston for the full pumping distance of its stroke. It will beappreciated that at the top of stroke, the piston is removed from thepumping chamber 19 and is positioned in the pre-dispense chamber so thematerial in the pre-dispense chamber can flow into the pumping chamber.In a typical application, vertical movement of the piston during itsstroke may be on the order of 0.050 inches.

The piston is received in a coupling member 21 which in turn is bushedinto a cap 22 bolted to the dispense housing 23. The coupling member 21is reciprocal within the cap and, as illustrated, the piston may bethreaded into a threaded bore in the coupling member.

Positioned above the dispense sub-assembly is an actuator sub-assembly30 which includes a linear actuator 31 which drives a rod 32 which iscoupled to the coupling member 21.

To provide for ease of disassembly of the two sub-assemblies, the rod 32may be driveably connected to the coupling member 21 through areleasable connection such as a magnetic connector using a magnet 33.Other types of quick disconnect may be provided such as, for example, asnap lock or ball lack where automatic connection will occur when therod is forced towards the coupling member and automatic disconnectioncan occur when the rod is pulled away form the coupling member with aforce sufficient to overcome the lock. Where a magnetic connection isemployed, as will be apparent, the magnet may be a permanent magnet,particularly in those instances when the coupling member 21 is formed offerrous material. Alternatively, mating, but opposite high strengthmagnets may be carried by the coupling member 21 cooperating with themagnet 33 in the rod end. Alternatively, if desired, the magnet 33 maybe an electromagnet controlled by an on/off switch to allow for positivecoupling and uncoupling of the drive rod 32 and coupling member 21.

The variable linear actuator 31 may be chosen from commerciallyavailable electronic actuators including those operating on magneticprincipals, mating thread principals operated by stepper motors or thelike, ball threads, etc. Preferably, the variable linear actuator willhave the following capabilities. It must be fast-acting, over therelatively short range of travel involved, it must be capable of beingstopped, and started, at any position along its travel, it must bereversible, it must be powerful enough to dispense the most viscousmaterial. Preferably, both its speed and force will be controllable. Acurrently available actuator model is available from BEI Sensors &Systems Company, Kimco Magnetics Division, San Marcos, Calif., and isbelieved to be described in U.S. Pat. No. 5,345,206, the teachings ofwhich are herein incorporated by reference. As used herein the termvariable linear actuator refers to those types of actuators which canimpart a linear movement to the piston and which can be electronicallycontrolled to vary stroke distance without requiring manual adjustment.

As shown in FIG. 2, the rod 32 is coupled to an axially moving portion34 of the linear actuator which in turn is carried in a stationaryportion 35 which is fixed to a bracket 36 which in turn is carried by asupport 37 which also carries a bracket 38 to which the dispensesub-assembly is mounted, as by bolts. A position sensing wand or rod 40is fixedly attached to the rod 32 and passes through the actuator 31 andbracket 36 to a sensor 41. As illustrated, this sensor may include anLED 42 and a photo detection sensor 43. As best shown in FIG. 3, thewand 40 passes between the LED 42 and the sensor 43 variably occludinglight passage. Thus, the quanta of light sensed by the sensor 43 isproportional to the position of the wand between maximum and minimumlevels. It will be apparent to those skilled in the art that this typeof a sensor will indicate a maximum transmission of light when thepiston is at its lowest position and a minimum transmission of lightwhen the piston is at its highest position, with determinablesensitivities at any point between those positions. This allows both theposition of the piston to be known instantaneously, as well as thedirection of movement (increasing or decreasing light intensity), rateof change of movement (ΔV) and speed.

Although I have shown the use of an LED-powered sensor, it will beunderstood that other types of position indicating sensors may beutilized such as, for example, an encoder, a potentiometer, a gearconnection to a rotary position sensor, variable pneumatic pressuresensor or other type of position indicator. Moreover, although I haveshown the sensor as being positioned on the opposite side of theactuator from the dispense sub-assembly, it would be appreciated that itcould be positioned in any convenient place, such as, for example injuxtaposition to the rod, reading indices marks on the rod.

Through a control system such as that illustrated in FIG. 1, thecombination of a sensor sensing position and movement of the piston,directly or indirectly, with a variable actuator allows for extremeversatility in dispensing. As illustrated, a power supply 50 providespower both to the position sensor assembly 51 and an amplifier 52providing power to a servo actuator 53 or other drive structure drivingthe actuator. A computer control 57 receives inputs from the positionsensor both with respect to a reference signal indicative of LED currentphoto metric output on line 53 and a position signal on line 54. Thecontrol can therefor compensate for LED aging by comparing the signal online 53 to a base or to a history. The computer 57 may receive bothcommand data inputs 55 and control signal inputs and outputs through abi-directional connection 56. It will be apparent to those skilled inthe art that many various subsidiary servo algorithms well known in theart may be employed to provide the various computations to output thedesired signals to the actuator. It is believed that standardproportional integral differential (PID) servo algorithms can beutilized to generate desired output signals. The computer control centermay, for example, consist of separate programmable controllers and microcontrollers with the micro controllers interfacing between commandsignals from the computer or other programmable controller and outputsignals to the amplifier in dependent response to received signals fromthe position sensor.

Among the information to be provided is a command to move the piston tothe full up (TDC) position, a command to dwell at either the full upposition or any intermediate position, the dwell being desired to allowthe material to flow into the pumping chamber from the pre-dispensechamber, movement direction commands between up and down, a full down(BDC) position, which may be desired when the dispense system is at restso as to prevent flow of material into the pumping chamber, and commandsignals for velocity, acceleration and actuator force. It will beappreciated that signals from the micro processor via the bi-directionalconnection 56 will provide performance related information that can becompared to expected performance to allow for performance adjustmentautomatically. Additionally, timing signals controlling the rate ofreciprocation will be provided. Further, as explained below, adisconnect position my also be programmed with the actuator raised abovethe TDC position of the piston.

At extremely short time intervals, the position of the wand is read viathe position signal and is compared to the position desired at thatinstant in time. An error signal derived from that comparison can thenbe processed into control signals to the actuator. The computer maystore historic position information to be compared with currentinformation to determine speed, acceleration, and change in position.The amplifier can be controlled to moderate the force generated by theactuator.

The use of closed-loop feed back to establish continuous real timeposition control of the piston provides programmable and enhancedcapabilities to the dispenser. For example, the up stroke adjustment isnow programmable allowing optimization of piston pull back distance tomaximize dispense speed. The use of an electronic actuator allowssubstantially greater speeds than pneumatic actuators. The down strokebeing similarly adjustable by programming allows for variable dispensevolumes per stroke controlled by programming on a dot by dot basis. Thisallows not only individual dot size control, but dot sizereproducibility and variability. For example, a sculptured thickness, orwidth, of the dispensed material can be provided. This may be beneficialwhere, for example, it is desirable to lay down a bonding pattern toattach a component to a substrate minimizing extrusion beyond thedimensions of the component. In such an instance, a greater thickness ofmaterial can be laid down in the central areas of the component withlesser quantities toward the periphery.

Programmable velocity control allows for control of discharge velocityof the material from the dispense tip which is advantageous,particularly when using viscous materials dispensed onto fragile parts.Additionally, the programmability of acceleration allows the unit toaccommodate sheer sensitive materials. Additionally, programmable forcecontrol to the actuator allows for variability in material viscosity andpressure sensitive materials. When coupled with output from the positionsensor, the device may be made self cleaning in that a partial blockagecan be sensed which may be cleared by a higher pressure shot or, uponfailure to move the piston at forces approaching the maximum safe forcefor the material or a drop off in force required for movement such asmay be caused by void or a bubble, the control can send a warning signalstopping operation before dispenser failure occurs. By monitoring theapplied force, i.e. amplified output, and comparing it to pistonmovement changes, the system can sense changes in viscosity.

Additionally, by providing programmable control of the dispenseoperation, numerous other features and capabilities can be provided. Forexample, the actual position and condition of the dispensed material maybe observed by means such as optical scanning and the like and be usedto provide an immediate feedback to the control to provide bothon-the-fly adjustments of dispense as well as to provide criticalquality control allowing the system to return to an under deposited areaand dispense additional material or to provide performance monitoring.In addition, the system can be made self calibrating. At start up, or atperiodic intervals, test deposits can be made at different settings andsensed optically. Differences from standards or among the tests can bedetected and used to calibrate the system. As shown in FIG. 1, by aimingan optical scanner or camera 70 at the work piece 71 below the tip 11and providing output signals 72 to the computer, the actual deposit canbe monitored, adjusted and compared to expected, desired or standardresults. The computer then can adjust the variable linear actuator 31 asdesired to maintain or obtain proper depositation. Control software forcomparing stored digitized information to scanned current images and foruse of such comparisons is well known to those skilled in the art and iscommon in manufacturing.

As shown in FIG. 4, the actuator 31 is preferably provided with anadditional full up position beyond the full up position for operation ofthe piston 13. This additional full up position decouples the rod 32from the coupling member 21 at the magnet connection. This allows theentire dispense sub-assembly 12 to be removed from the bracket forcleaning, replacement or service without requiring any access to theactuator sub-assembly.

It will therefore be appreciated that this invention substantiallyimproves the art of small quantity viscous fluid dispensing utilizingreciprocating pistons and provides a fully programmable dispenser whereper stroke dispense volume, velocity of dispense, rate of dispense andforce of dispense are all variably controlled by utilizing a variablelinear actuator for driving the piston combined with a position sensingindicator and an appropriate control system. Additionally, the inventionprovides a unique method of coupling the actuator to the dispensesub-assembly allowing ease of maintenance and switch-out of material.

Although I have shown my invention in connection with the description ofa preferred embodiment, it would be readily apparent to those of skillin the art that numerous alternatives may be unitized in place of theindividual components I have chosen to illustrate. For example, althoughI have utilized a linear actuator positioned co-axially with the piston,it will be appreciated that other arrangements are substitutable. Forexample, the power section of the actuator may be positioned other thanco-axial and may use a drive connection other than linear. A rotaryactuator could operate a reversible rotary cam driving against a faceconnected to the coupling member either employing a cam track connectionor a return spring or, as another example, the actuator could beelectric driven such as available from Physik Instruments in Germany.Additionally, although I have shown a single piston and single dispensetip, others may wish to utilize multiple piston, multiple dispense tipconstructions or different piston tip assemblies.

1. A system for dispensing viscous fluids in small quantities comprisinga recipricatable piston coupled to a variable actuator, a programmablecontroller operatively connected to the actuator, a position sensorsensing the position of the piston and outputting a signal to thecontroller reflecting the substantially instantaneous position of thepiston, the controller including a computer for comparing pistonposition signals to pre-determined criteria and outputting controlsignals to the variable actuator in dependent response thereto.
 2. Asmall quantity viscous fluid dispense assembly comprising a reciprocalpiston aligned with a dispense orifice effective to force materialthrough said orifice during a dispense stroke of the piston, a variablelinear actuator operatively connected to the piston for driving thepiston, a position sensor effective to sense the instantaneous positionof the piston, a computer control controlling activation of the variablelinear actuator, the computer control effective to vary dispense strokemovement distance electronically.
 3. The system of claim 1 wherein thecontrol signals are effective to modify subsequent movement of thepiston in at least one of piston stroke distance, piston stroke speed,piston stroke acceleration and piston stroke force.